The addition of carbon monoxide to olefins (carbonylation) has long been considered in the art to be a highly attractive route to a number of commercially valuable chemical products. It is known in the art to prepare unsaturated aliphatic carboxylic acids and their esters by the catalytic oxidative carbonylation of an olefin. More particularly, it is known to synthesize aliphatic carboxylic acids and their esters by reacting carbon monoxide, oxygen and an olefin such as octene or propylene under elevated temperature and pressure conditions in the presence of various catalysts, often in the presence of dehydrating agents. One useful type of ester is an alkyl succinate which is a precursor for alkyl succinic anhydrides or diols. The related polyakenyl succinic anhydride is used for lubricating oil additives and for polyester resins.
Some of the early patents in the field, such as U.S. Pat. Nos. 3,397,226, 3,397,225, 3,481,845 and 3,755,421, demonstrate the use of catalysts comprising a platinum group metal salt or chelate and a multivalent heavy metal salt which functions as a redox agent for the oxidative carbonylation of hydrocarbon olefins to produce esters of unsaturated carboxylic acids, esters and dicarboxylic acids and esters of beta-alkoxy-substituted carboxylic acids.
In another process which is disclosed in J. Org. Chem. 1979, 44(20), 3474-82, methoxycarbonylation of a variety of olefins with methanol and carbon monoxide takes place in the presence of palladium, using stoichiometric amounts of copper(II) chloride as a reoxidant, and sodium butyrate as a buffer. Different aliphatic carboxylic acid diesters were formed in varying yields depending on the choice of diolefin and the carbon monoxide pressure. The reaction usually resulted in the addition of two carbomethoxy functions to the double bond.
In J. Am. Chem. Soc. 98, 1810 (1976), James and Stille provide much data on the yields of various esters using different cyclic and acyclic olefin reactants. They also discuss the effects of some of the cocatalysts, etc. used in many of these reactions and yields of products. Again palladium(II) chloride is employed as catalyst, and stoichiometric amounts of copper(II) chloride is used as reoxidant. The effect of added base is also discussed.
A study reported in J. Org. Chem. 37 2034 (1972) discussed experiments which demonstrate that in a palladium redox system, optimum results are achieved by restricting both amounts of excess hydrogen ion and chloride ion.
U.S. Pat. No. 4, 281,174 discloses a catalyst system for preparing dimethyl oxalates by the oxidative carbonylation of alcohol which involves the reaction of CO, air and alcohol. Dimethyl carbonate can also be produced by a similar Pd catalyst.
In many processes known in the art separation of the high boiling aliphatic carboxylic acid or ester product from the catalyst system can be difficult. It would be advantageous to devise a catalyst system which is heterogenous, which improves the product distribution to desired carboxylic acid and which improves ease of product/catalyst separation. A supported (palladium-containing) catalyst system which allowed for easier separation of product from catalyst by filtration would be more efficient and far more attractive commercially. Furthermore, the selection of a suitable support for such a palladium catalyst system may be made so as to improve both the productivity to desired carboxylic acid/ester derivative and the selectivity to said desired product or products.